The present invention relates to power supply apparatus and methods and, more particularly, to uninterruptible power supply (UPS) apparatus and methods.
Any of a variety of different architectures may be used in a UPS, including online, standby and line interactive architectures. Such UPS architectures are described, for example, in U.S. Pat. No. 6,314,007 to Johnson.
A typical on-line UPS includes a combination of a rectifier and inverter linked by a DC link. An AC utility source is typically coupled to the rectifier, which responsively produces a DC voltage on the DC link. The inverter typically generates an AC output voltage for a protected load from the DC voltage on the DC link. An ancillary DC power source is typically coupled to the DC link to provide power to the inverter in the event that the AC utility source fails.
Some online UPSs may include a bypass circuit, which may be used to directly couple the AC utility source to the load. The bypass circuit may be used, for example, for purposes of deactivating the rectifier and/or inverter for maintenance actions and/or to provide power to the load when the rectifier and/or inverter fails. Such a bypass circuit may also be used to provide a “high efficiency” mode of operation, as described, for example, in U.S. Pat. No. 6,295,215 to Faria et al. An online UPS may also provide power conditioning (e.g., power factor correction) in a bypassed mode using the inverter and/or rectifier, as described, for example, in U.S. Pat. No. 6,295,215 to Faria et al and U.S. Pat. No. 6,906,933 to Taimela.
A variety of techniques have been proposed for reducing input current harmonic distortion and/or improving power factor for a UPS. For example, PCT International Application Publication WO 94/14228 to Oughton describes techniques for operating a pulse width modulated (PWM) converter wherein occurrence of a notch portion of the input current to the converter is determined, control signals are generated in response to switch a plurality of bi-directional switches of the PWM converter so that the input current is modified only during the notch portion. The current may be modified to a generally sinusoidal shape so that the total harmonic distortion of the input current is limited. U.S. Pat. Nos. 6,262,899, 6,400,586 and 6,661,678 to Raddi et al. describe various power factor correction circuits for UPS systems.